Worm gear mechanisms belong to the standard gear mechanisms and are usually used as step-down gear mechanisms, high step-down ratios being possible by way of the worm gear mechanism. For example, relatively rapidly rotating electric motors can be used for slow adjustment movements by way of the high step-down ratio which can be realized by way of the worm gear mechanism, a high torque being provided for the adjustment movements. Worm gear mechanisms of this type are used in automotive applications, for example, in electric power steering systems, in window lifter drives or in sunroof drives.
The worm gear mechanisms usually have a worm gear and a gearwheel which engages into the worm gear, the worm gear being driven by an electric motor via a drive shaft, and the gearwheel being connected fixedly to an output shaft so as to rotate with it. The worm gear mechanism can be configured with a second step-down stage for a higher step-down ratio.
For a long service life of the worm gear mechanism, the backlash between the worm gear and the gearwheel which engages into the worm gear should be set in an optimum manner. If the backlash is set to be too great or too small, this results in increased wear which reduces the service life of the worm gear mechanism. In order to ensure the optimum backlash at any time, it is known from the prior art to prestress the worm gear axially. For example, DE 10 2007 038 916 A1 describes a belt tensioner drive for a safety belt, the belt tensioner drive having an electric motor and a double worm gear mechanism. The electric motor drives a worm gear via a rotor shaft, which worm gear engages into a gearwheel which is arranged on an intermediate shaft, the intermediate shaft additionally having a second worm gear which is operatively connected to a second gearwheel. The second gearwheel is connected fixedly to a gear mechanism output shaft so as to rotate with it. In order to set the correct backlash, the belt tensioner drive has an axially prestressed pot bearing, in which the rotor shaft is mounted. The prestress takes place by way of a spring element which is arranged between the axially displaceable pot bearing and the rigid housing. It is a disadvantage of said embodiment that the gear backlash is compensated for via the axially displaceable pot bearing which is prestressed via a spring element, the pot bearing absorbing axial and radial loads, and the sliding faces of the pot bearing and the housing which bear against one another being subject to wear in the case of an axial displacement of the pot bearing, as a result of which the service life of the worm gear mechanism is reduced.